Theoretical study of spectroscopy and dissociation of SO 2 Br 2 and SO 2 I 2 Deepanwita Ghosh, Bhaskar Mondal, Abhijit Kumar Das * Department of Spectroscopy, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India article info Article history: Received 15 June 2009 In final form 17 June 2009 Available online 21 June 2009 abstract Spectroscopy and dissociation of the sulfuryl halides SO 2 Br 2 and SO 2 I 2 have been studied in detail using ab initio MP2 and CCSD(T) methods. The discrepancy among the recent theoretical works for the assign- ment of harmonic vibrational frequencies of SO 2 Br 2 has been addressed. The possibility of various disso- ciation channels has been explored considering that the fragmented atoms and molecules can stay in their ground state. Only halide producing channels have been studied from thermodynamic point of view. Interesting pattern has been observed in their dissociation energy spectra for the dissociation channels. Finally, the enthalpy of formation and stability of these molecules have been discussed. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Several studies, mostly experimental, have been made on sulfu- ryl halides SO 2 F 2 and SO 2 Cl 2 on their structural and spectroscopic properties because of their wide range of applications in diverse fields, mainly in industry as chlorinating or sulfonating agents for manufacturing of intermediates that are further used in different areas such as plant protecting agents and biocides, pharmaceuti- cals and fine chemicals. But no experimental work has been done so far on SO 2 Br 2 and SO 2 I 2 molecules. The theoretical work on SO 2 Br 2 is very limited. As far as our knowledge goes, no theoretical attempted has been made to study SO 2 I 2 . Kowal [1] computed the equilibrium geometries and anharmonic vibrational spectra of sul- furyl bromide SO 2 Br 2 using MP2 (FC) method in conjunction with 6-31G(df), effective core potential (ECP) SBKJC(3df), cc-pVTZ and cc-pV(T + d) basis sets and assigned their vibrational modes. Fer- nandez et al. [2] carried out both theoretical and experimental study on SO 2 F 2 and SO 2 Cl 2 but performed only theoretical work on SO 2 Br 2 . Force fields and vibrational wavenumbers were calcu- lated for these molecules using DFT techniques. The assignment of Fernandez et al. [2] for the harmonic vibrational frequencies of SO 2 Br 2 differs from that made by Kowal [1]. Moreover no theoret- ical and experimental works have been done to investigate their dissociation processes. In this Letter three important problems namely, spectroscopy, dissociation and stability of SO 2 Br 2 and SO 2 I 2 have been investigated in detail. 2. Computational details Spectroscopy, dissociation and thermochemistry of SO 2 Br 2 and SO 2 I 2 molecules have been studied in detail using second order Möler–Plesset perturbation (MP2) theory and coupled cluster CCSD(T) method [3,4]. The electron correlation effects have been taken into account via second order Möler–Plesset perturbation theory and coupled cluster CCSD(T) method which includes single and double excitations and an estimate of triple excitations by a perturbation treatment. We used coupled cluster CCSD(T) method [4] in conjunction with the VDZP basis set of Huzinaga et al. [5] for calculating various thermodynamic parameters for halogen pro- duction channel. We also applied MP2 method to calculate the heat of formation of these molecules using atomization scheme. Five basis sets are used to check the consistency and accuracy of the calculated values. For the calculation of geometrical parameters and harmonic vibrational frequencies of SO 2 Br 2 and SO 2 I 2 contain- ing heavy atoms we used first four basis sets. The composition of the five basis sets is as follows: BS1 = cc-pVTZ [6] basis set for S, O and cc-pVTZ for Br/Sadlej- pVTZ [7] for I. BS2 = cc-pVQZ [6] basis set for S, O and Br. BS3 = cc-pVTZ basis set for S and O and pseudo potential cc- pVTZ-pp basis set [8] for the heavy Br and I. BS4 = aug-cc-pVTZ [6] basis set for S and O and the pseudo po- tential aug-cc-pVTZ-pp basis set [8] for the heavy Br and I. BS5 = VDZP basis set of Huzinaga [5] for S, O and Br/I The dissociation energy is calculated using MP2 method in con- junction with BS1 basis set. Enthalpy of formation at 0 K is esti- mated using atomization scheme in the following way: DH 0 f ;0 ðSO 2 X 2 Þ¼DH 0 a þ DH exp f ;0 ðS ðgÞ Þþ 2DH exp f ;0 ðO ðgÞ Þþ 2DH exp f ;0 ðX ðgÞ Þ; ð1Þ where DH exp f ;0 is the experimental heat of formation of the corre- sponding atom. DH 0 a is the computed atomization energy of SO 2 X 2 for the atomization reaction at 0 K SO 2 X 2ðgÞ ! S ðgÞ þ 2O ðgÞ þ 2X ðgÞ ð2Þ 0009-2614/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2009.06.047 * Corresponding author. Fax: +91 33 24732805. E-mail address: spakd@iacs.res.in (A.K. Das). Chemical Physics Letters 477 (2009) 28–31 Contents lists available at ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett